Catalytic production of dimethyl sulfide

ABSTRACT

Process for the catalytic production of dimethyl sulfide in which dimethyl ether and hydrogen sulfide can be reacted in about equimolar amounts to achieve almost quantitative yields of dimethyl sulfide by carrying out the reaction in the presence of a catalyst consisting essentially of aluminum oxide having a superimposed layer of up to about 10 percent by weight of silica applied thereto.

United States Patent Meyer et al.

3,686,328 [451 Aug. 22, 1972 CATALYTIC PRODUCTION OF DIMETHYL SULFIDE Inventors: GerhardMeyer, Obernburg; Helmut Magerlein; Hans-Dieter Rupp, both of Erlenbach, all of Germany Assignee: Glamstoff AG, Wuppertal, Germany Filed: Aug. 11, 1969 Appl. No.: 849,199

Foreign Application Priority Data Aug. 10, 1968 Germany ..P 17 93 173.6

US. Cl. ..260/609 A, 252/451, 252/455 R,

260/632 B Int. Cl ..C07c 149/14 Field of Search ..260/609 A [56] References Cited UNITED STATES PATENTS 2,951,873 /1960 Folkins et al. ..260/609 A Primary Examiner-Joseph Rebold Assistant Examiner-D. R. Phillips Attorney.1ohnston, Root, OKeeffe, Keil, Thompson & Shurtleff 5 7 ABSTRACT 9 Claims, No Drawings CATALYTIC PRODUCTION OF DIMETHYL SULFIDE A reaction of methanol with hydrogen sulfide in sucha .manner that dimethyl sulfide is obtained as themain product (see German Pat. No. 962,789). However, in this case a considerable amount of methyl mercaptan is also obtained as a by-product and must be separated in a cumbersome and difficult process.

The reaction of dimethyl ether with hydrogen sulfide in the presence of certain catalysts for the production of dimethyl sulfide has also been described in the prior art. Thus, German Pat. No. 1,016,261 recommends the use of sulfides of metals of Group VI of the Periodic System as catalysts for this reaction, although this particular process provides a yield of the dimethyl sulfide ofonly about 84 percent. An increase in this yield is possible only by recycling the off-gas and using an excess of the dimethyl ether.

In Canadian Pat. No. 553,412, a process for the production of dimethyl sulfide is described in which dimethyl ether and hydrogen sulfide are reacted in the presence of aluminum or thorium oxides or mixtures thereof as the essential catalyst. These catalysts contain polyvalent metals which have a greater afiinity for oxygen than for sulfur. If desired, there can be intermixed with these catalysts various inert substances such as silicon dioxide. It is indicated that it is advantageous to employ a catalyst produced by calcining and milling bauxite and then treating with a solution of caustic soda in such a manner as to convert the bauxite into sodium aluminate. From this, the aluminum oxide is finally again precipitated. Moreover, one catalyst is mentioned which consists of an activated technical aluminum oxide gel admixed with about 5 percent silicic acid.

The reaction of dimethyl ether with hydrogen sulfide proceeds according to the known processes at temperatures between 320C. and 450C. I

In order to achieve good yields with reference to the added hydrogen sulfide, the dimethyl ether must be employed in excess amounts which must again be separated from the final product. To also achieve as quantitative a reaction as possible with respect to the dimethyl ether, it becomes necessary to separate the non-reacted initial materials from the gases leaving the reaction zone and to lead these recovered materials back into the reaction zone. This, of course, represents a very troublesome procedure.

In following the known process, e.g., according to the above-noted Canadian Patent, it has been established that the yields drop off very sharply with the use of temperatures below 350C. However, for the conversion of dimethyl ether with hydrogen sulfide into dimethyl sulfide, it is desirable to carry out the reaction at the lowest possible temperatures since the formation of decomposition products increases with raised temperatures, e.g., as with a cracking gas. It will be quite apparent that not only will the yields be reduced by higher temperatures, but also the substances formed as by-products by the thermal decomposition must be separated in additional or separate process steps. Moreover, the thermal decomposition causes the formation of elementary carbon which deposits on the catalyst in the form of coke and thus substantially reduces the activity and life of the catalyst.

One object of the present invention is to provide a catalytic process for the production of dimethyl sulfide from dimethyl ether and hydrogen sulfide which will give almost quantitative yields with reference to both of the initial reactants at temperatures below about 350C. Another object of the invention is to avoid the formation of by-products, including coke deposits. These and other objects and advantages of the invention will become more apparent upon consideration of the following detailed specification.

It has now been surprisingly found in accordance with the invention that excellent yields of dimethyl sulfide can be achieved by reacting dimethyl ether with hydrogen sulfide, preferably in a molar ratio of approximately 1:1, in contact with a catalyst consisting essentially of aluminum oxide activated by a layer of about 0.2 to 10 percent by weight, preferably about 0.2 to 3 percent by weight, of silica superimposed thereon. The reaction proceeds best at a temperature of about 310C. to 350C.

The preparation of the catalyst to be used in the process of the invention can be accomplished in a number of ways. In all cases, however, it is essential to activate the aluminum oxideby depositing or superimposing silica on the surface thereof, preferably by depositing silicic acid onto the aluminum oxide using silicon tetrachloride and water or sodium silicate and hydrochloric acid and washing neutral as well as drying to achieve a neutral-reacting, silica-coated aluminum oxide catalyst.

The following method of preparing the catalyst is especially suitable. A pure aluminum oxide is first treated with an aqueous sodium silicate solution (waterglass). It is then evaporated to dryness. Next the coated aluminum oxide is treated with hydrochloric acid and washed neutral with distilled water. Finally, the neutral catalyst is dried and can be used directly in the reaction according to the invention.

One can also treat a moist, pure aluminum oxide with silicon tetrachloride which has been diluted with hexane and then wash the treated material neutral with water. The silicon tetrachloride reacts with the water of the moistened or wctted aluminum oxide so as to deposit silicic acid onto the oxide. After washing with distilled water until there is a neutral reaction of the wash water, the resulting product is dried and ready for use.

The aluminum oxide used for the catalyst must be pure and should not contain any alkaline residues. The particle size of the aluminum oxide can vary within wide limits, for example from about 0.1 to 10 mm.

It has proven to be especially advantageous for purposes of the invention to use an aluminum oxide which has been activated with a superimposed layer of 0.2 to 5 percent by weight of silica. Nevertheless, it will be understood that even larger amounts of silica can be used with reference to the aluminum oxide substrate or catalytic carrier. For example, catalysts with a superimposed layer of percent by weight of silica have also proven to be useful. Thus, while it is believed that the aluminum oxide becomes activated by the silicic acid or silica deposited thereon, the reverse may also be true, i.e., that the silica becomes combined in some manner with the aluminum oxide to form active sites on the catalyst surface.

It is quite important to wash the catalyst until neutral after depositing the silicic acid as SiO onto the aluminum oxide so that there is no residue of hydrochloric acid. Likewise, alkaline residues must be avoided in the finished catalyst as well as in the initial aluminum oxide. Good results cannot be assured except with a substantially neutral-reacting catalyst.

After the prepared catalyst has been dried, it can first be subjected to a heat treatment at temperatures of about 300400C. prior to the reaction of the dimethyl ether with hydrogen sulfide. This preheating step appears to improve the mechanical stability and coherence of the catalyst, i.e., so that the silica layer remains firmly attached to the aluminum oxide.

For carrying out the process according to the invention, the catalyst is introduced into a suitable reactor, e.g., a vertically arranged reaction tube adapted to receive a catalyst bed. The reaction zone can be heated by any suitable means, e. g., a heating jacket or the like, to a temperature which is preferably adjusted between about 310 and 350C. Before their entry into the reaction zone, the gaseous reactants are preferably preheated to about 250C. to 300C. The hydrogen sulfide and dimethyl ether are most advantageously introduced in equimolar amounts into the reaction zone for passage in contact with the catalyst. Although the catalyst loading, i.e., the throughput amount of dimethyl ether per ml. of catalyst per hour, can be varied over a relatively wide range, it has proven to be especially advantageous to carry out the reaction with a throughput of about 0.2 to 0.3 grams of dimethyl ether per ml. of catalyst per hour.

A practically quantitative conversion is achieved with the process according to the invention without it being necessary to recycle gases back into the reaction zone. The selectivity is outstanding; thus, by using a catalyst of aluminum oxide with a superimposed layer of 2 percent by weight SiO and a throughput of 0.223 grams of dimethyl ether per ml. of catalyst per hour (and an equimolar throughput of hydrogen sulfide), there is obtained a yield of 97.8 percent.

The proportion of by-products is extremely small and amounts to not more than about 2 percent. The recovery of the reaction product can be accomplished very easily. Since the temperature of the reaction is relatively low, i.e., capable of being maintained below about 350C., a thermal decomposition can be substantially avoided, i.e., so that very little or practically no by-products are formed according to the equation:

CH3OCH3 CH4 H2.

Also, a deposition of carbon which reduces the activity of the catalyst is practically completely prevented. A long catalyst life can thus be achieved so as to maintain high yields over an extended period of time.

The invention is further illustrated by the following examples.

EXAMPLE 1 Into the middle of a 560 mm. long glass tube having an inner diameter of 35 mm. there is introduced 30 ml. of a catalyst which consists of a neutral aluminum oxide with a superimposed layer of 2 percent by weightof SiO While maintaining a temperature of 320C. in the reaction zone, a mixture of 6.69 grams of dimethyl ether and 4.86 grams of hydrogen sulfide per hour are conducted over the catalyst. The conversion amounts to 99.5 percent of which the reaction products are 97.8 percent dimethyl sulfide, 2 percent methyl mercaptan and 0.2 percent methanol.

EXAMPLE 2 Using the same reaction conditions as'in Example 1, the catalyst consisted of aluminum oxide bearing a superimposed layer of 5 percent by weight SiO The conversion amounted to 98 percent. The proportions of this almost total conversion were as follows: dimethyl sulfide=98 percent; methyl mercaptan=l.4 percent; and methanol=0.6 percent.

If one proceeds under the same reaction conditions as in the preceding examples but using only the aluminum oxide without the SiO layer, then the conversion amounts to only 73.1 percent with the reaction products consisting of 69.8 percent dimethyl sulfide, 26.3 percent methyl mercaptan and 3.8 percent methanol.

On the other hand, if the same reactions are used but with an homogeneous mixture of aluminum oxide containing 2 percent by weight SiO distributed therein, then the conversion amounts to only 50.7 percent. The conversion products are distributed as follows: dimethyl sulfide=69.4 percent; methyl mercaptan=23.3 percent; and methanol=7.5 percent.

The invention is hereby claimed as follows:

1. In a process for the production of dimethyl sulfide by catalytically reacting dimethyl ether with hydrogen sulfide at an elevated temperature, the improvement which comprises carrying out said reaction at a temperature of about 310C. to 350C. in contact with a neural-reacting catalyst consisting essentially of aluminum oxide activated by a layer of about 0.2 to 10 percent by weight of silica superimposed thereon, said catalyst being obtained by depositing a layer of silicic acid on the surface of the aluminum oxide,'washing neutral and drying the resulting coated product.

2. A process as claimed in claim 1 wherein the amount of silica superimposed onto said aluminum oxide is about 0.2 to 3 percent by weight.

3. A process as claimed in claim 1 wherein the dimethyl ether and the hydrogen sulfide are reacted in a molar ratio of approximately 1:1.

4. A process as claimed in claim 1 wherein about 0.2 to 0.3 grams of dimethyl ether are reacted per hour and per milliliter of catalyst with an approximately equimolar amount of hydrogen sulfide.

5. A process as claimed in claim 4 wherein the amount of silica superimposed onto said aluminum oxide is about 0.2 to 3 percent by weight.

6. A process as claimed in claim 1 wherein said catalyst is a substantially neutral reacting, silica-coated aluminum oxide obtained by depositing silicic acid onto the surface of the aluminum oxide using silicon tetrachloride and water or sodium silicate and then drying and neutralizing the coated aluminum oxide.

grams per milliliter of catalyst per hour.

9. A process as claimed in claim 1 wherein said catalyst is obtained by first treating the aluminum oxide with an aqueous sodium silicate solution and evaporating to dryness, then treating the resulting coated aluminum oxide with hydrochloric acid and thereafter washing neutral and drying the resulting coated product. 

2. A process as claimed in claim 1 wherein the amount of silica superimposed onto said aluminum oxide is about 0.2 to 3 percent by weight.
 3. A process as claimed in claim 1 wherein the dimethyl ether and the hydrogen sulfide are reacted in a molar ratio of approximately 1:1.
 4. A process as claimed in claim 1 wherein about 0.2 to 0.3 grams of dimethyl ether are reacted per hour and per milliliter of catalyst with an approximately equimolar amount of hydrogen sulfide.
 5. A process as claimed in claim 4 wherein the amount of silica superimposed onto said aluminum oxide is about 0.2 to 3 percent by weight.
 6. A process as claimed in claim 1 wherein said catalyst is a substantially neutral reacting, silica-coated aluminum oxide obtained by depositing silicic acid onto the surface of the aluminum oxide using silicon tetrachloride and water or sodium silicate and then drying and neutralizing the coated aluminum oxide.
 7. A process as claimed in claim 6 wherein the catalyst has been preheated at temperatures of between about 300*C. and 400*C. prior to being used in said reaction of dimethyl ether with hydrogen sulfide.
 8. A process as claimed in claim 1 wherein said aluminum oxide contains about 0.2 to 5 percent by weight of silica deposited thereon, and the two reactants are conducted in a molar ratio of about 1:1 over said catalyst at a temperature of about 310C. to 350*C. with a throughput of dimethyl ether of about 0.2 to 0.3 grams per milliliter of catalyst per hour.
 9. A process as claimed in claim 1 wherein said catalyst is obtained by first treating the aluminum oxide with an aqueous sodium silicate solution and evaporating to dryness, then treating the resulting coated aluminum oxide with hydrochloric acid and thereafter washing neutral and drying the resulting coated product. 